title: The central Sirtuin 1/p53 pathway is essential for the orexigenic action of ghrelin.
abstract: OBJECTIVE
  Ghrelin is a stomach-derived peptide that increases food intake through the activation of hypothalamic AMP-activated protein kinase (AMPK). However, the molecular mechanisms initiated by the activation of the ghrelin receptor, which in turn lead to AMPK activation, remain unclear. Sirtuin 1 (SIRT1) is a deacetylase activated in response to calorie restriction that acts through the tumor suppressor gene p53. We tested the hypothesis that the central SIRT1/p53 pathway might be mediating the orexigenic action of ghrelin.
  
  
  METHODS
  SIRT1 inhibitors, such as Ex527 and sirtinol, and AMPK activators, such as AICAR, were administered alongside ghrelin in the brain of rats and mice (wild-type versus p53 knockout [KO]). Their hypothalamic effects on lipid metabolism and changes in transcription factors and neuropeptides were assessed by Western blot and in situ hybridization.
  
  
  RESULTS
  The central pretreatment with Ex527, a potent SIRT1 inhibitor, blunted the ghrelin-induced food intake in rats. Mice lacking p53, a target of SIRT1 action, failed to respond to ghrelin in feeding behavior. Ghrelin failed to phosphorylate hypothalamic AMPK when rats were pretreated with Ex527, as it did in p53 KO mice. It is noteworthy that the hypothalamic SIRT1/p53 pathway seems to be specific for mediating the orexigenic action of ghrelin, because central administration of AICAR, a potent AMPK activator, increased food intake in p53 KO mice. Finally, blockade of the central SIRT1 pathway did not modify ghrelin-induced growth hormone secretion.
  
  
  CONCLUSIONS
  Ghrelin specifically triggers a central SIRT1/p53 pathway that is essential for its orexigenic action, but not for the release of growth hormone.
authors.affiliation: Department of Physiology, School of Medicine--Instituto de Investigaciones Sanitarias (IDIS), University of Santiago de Compostela, Santiago de Compostela, Spain.
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Velásquez
authors.forename: Gloria
authors.initials: G
authors.lastname: Martínez
authors.forename: Amparo
authors.initials: A
authors.lastname: Romero
authors.forename: María J
authors.initials: MJ
authors.lastname: Vázquez
authors.forename: Katia D
authors.initials: KD
authors.lastname: Boit
authors.forename: Iria G
authors.initials: IG
authors.lastname: Dopeso-Reyes
authors.forename: Miguel
authors.initials: M
authors.lastname: López
authors.forename: Anxo
authors.initials: A
authors.lastname: Vidal
authors.forename: Ruben
authors.initials: R
authors.lastname: Nogueiras
authors.forename: Carlos
authors.initials: C
authors.lastname: Diéguez
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D015153:Blotting, Western; D002227:Carbazoles / Q000494:pharmacology; D004435:Eating / Q000187:drug effects; D005247:Feeding Behavior / Q000187:drug effects; D054439:Ghrelin / Q000494:pharmacology*; D017403:In Situ Hybridization; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009284:Naphthols / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D056564:Sirtuin 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: C550547:6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide; D001549:Benzamides; D002227:Carbazoles; D054439:Ghrelin; D009284:Naphthols; D016159:Tumor Suppressor Protein p53; C439060:sirtinol; D055372:AMP-Activated Protein Kinases; D056564:Sirtuin 1